A method and a device for treating a waste liquid are already known from EP 0 142 018 B1, where the waste liquid consisting of a base liquid and non-evaporated solid impurities contained therein is loaded into a carrier gas stream. This mixture is then heated in an evaporator to a temperature above the saturation temperature of the water vapor produced in the heating process. The solid particles are separated from this overheated mixture of carrier gas and dry vapor in a separator unit. Starting out from the separator unit, the carrier gas is first compressed by means of a compressor and then conveyed through the evaporator in order to heat the mixture to be cleaned, consisting of carrier gas and waste liquid. At the same time the mixture of carrier gas and dry vapor, freed of impurities, cools in the evaporator as a result of its heat transfer. During this process the base liquid which is conveyed in the form of hot condensate to a heat exchanger for the preheating of the waste liquid condenses, while on the other hand the carrier gas is conveyed to the evaporator input where a mixing of carrier gas and preheated waste liquid takes place.
This method is suited to obtain solids and/or substances contained in a waste liquid that cannot be evaporated, thus achieving a degree of cleanliness of the departing vapor that is approximately equal to the degree of cleanliness of distilled water. It was found, however, that when a waste liquid is charged with essentially liquid impurities, such as e.g. oil-containing organic materials, incrustations may occur on the evaporator side of the heat exchanger, requiring frequent cleaning of the heat exchanger. In addition, considerable losses of carrier gas occur during the separation process, as well as during separation in the evaporator of carrier gas from condensate, which can have an adverse effect in the long run on an optimal execution of the process.
A method and device for the treatment of a waste liquid consisting of a base liquid and impurities contained therein is furthermore known from DE 197 41 806 A1. Here the waste liquid to be cleaned is dispersed in a carrier gas stream, preheated in a heat exchanger, and the impurities are then eliminated in the form of concentrate in a separator unit. The concentrate is post-dried at temperatures up to 170° C. in an evaporator with vent compression downstream of the concentrate separator unit, whereby the vent condensate is conveyed back into the overheated mixture of carrier gas and vapor and is mixed with it. The mixture of carrier gas and dry vapor cleaned after the separation of the impurities is then compressed in a compressor and is conveyed to a heat exchanger for the heating of the mixture of preheated waste liquid and carrier gas, whereby the base liquid condenses. This condensate is conveyed into a condensate collector in its form of a stripper and is atomized through a spray nozzle at that location. The volatile components liberated thereby are conveyed via a gas conduit through cooled water contained in a liquid container, whereby the water-soluble components are dissolved in the water while the remaining gas is let out into the surrounding air via an output conduit. The condensate produced in the stripper during atomization is collected on the bottom and is conveyed to a heat exchanger in which the still prevailing residual heat is transferred to the waste liquid to be cleaned in order to preheat it.
It is a disadvantage in this case that the carrier gas must be fed continuously into the system, because a large portion of the carrier gas is emitted directly into the surrounding air via the condensate collecting container.
The constant feeding of fresh carrier gas into the system is very expensive on the one hand, and on the other hand reduces the effectiveness of the overall installation considerably. Due to these considerable losses in carrier gas, expensive inert gas cannot be used as the carrier gas in such an installation because the operating costs would then become excessive. Such an installation can therefore be operated economically only with fresh air as the carder gas, but this is problematic because of the way certain components of the air can react with certain components of some waste liquids, so that the separation of the impurities dissolved in the waste liquid may become more difficult. For example, the oxygen contained in the carrier gas air is reduced in the case of wet oxidation so that carrier gas must be replenished by providing more air. This also means that an increased carrier gas output is required through the stripper in order to cover the needed oxygen requirement. Since the water reserve in the downstream cooling water container is also subjected to greater stress in that case, an undesirable output of vaporous materials contained in the carrier gas is produced and endangers the environment.
In addition, the residual gas emitted into the surrounding air via an output conduit typically still contains a considerable amount of volatile condensate impurities so that the environment is adversely affected.
Furthermore, it is a disadvantage here that only certain liquid impurities are separated. In case of treatment fluids with a plurality of liquid impurities having different boiling temperatures and containing relatively large quantities of gaseous impurities, the danger exists that a considerable portion of the liquid and/or gaseous impurities cannot be removed with this method and the desired treatment goal cannot be reached. This is because, depending on the treatment fluid, a significant portion of the liquid impurities remain in the base liquid after condensation to pollute the base liquid, while the gaseous impurities together with the carrier gas are emitted into the environment in an undesirable manner if they are not water-soluble. The danger of environmental pollution is potentially great in this case.
This method is therefore suitable on the whole only for the treatment of a very narrow spectrum of treatment fluids, requiring a great number of treatment fluids. Thus it is a particular disadvantage that this method is not suitable for obtaining drinking and service water from sea or brine water, since large quantities of CO2 are produced as the HCO3 disintegrates thermally, compounds which must be removed from the system and a task which is impossible for the above-mentioned method. By heating the vapors in the concentrate evaporator to temperatures up to 170° C., an evaporation of contents of the concentrate is achieved that are then precipitated in the form of exhaust vapors and are fed together with them into the mixture of carrier gas and dry vapor. As a result an undesirable second contamination of the mixture of carrier gas and dry vapor occurs thereby resulting in an undesirable pollution of the process when the vapor condenses.
From WO 01/03794 A1, a method and device are known for the treatment of a waste liquid in which the waste liquid consists of a base liquid and liquid impurities contained therein. In order to separate the liquid impurities, a mixture of waste liquid and carrier gas is evaporated into a wet mixture of carrier gas and dry vapor in such a manner that the base liquid is evaporated and the impurities having a higher boiling temperature than the base liquid are left over in the form of a residual liquid portion.
Following this, the wet mixture of carrier gas and vapor is conveyed to a concentrate separator unit in which the residual liquid portion is separated as a concentrate. The mixture of carrier gas and dry vapor, freed of residual liquid, is compressed and then cooled so that the base liquid is condensed and can be separated in a downstream condensate separator unit.
The carrier gas separated at the condensate separator unit is conveyed in a closed circuit in such a manner that a first partial mass flow of the carrier gas separated at the condensate separator unit is conveyed directly to the waste liquid in an admixing device. A second partial mass flow of the carrier gas separated at the condensate separator unit is conveyed through a gas dryer to be dried, and then in the form of dry carrier gas, conveyed again to the waste liquid in the admixing device.
Before the waste liquid is conveyed to the admixing device for the admixing of the carrier gas, a two-step pre-heating is effected by a condensate/waste liquid heat exchanger with the hot condensate coming from the condensate collecting container as well as by a concentrate/waste liquid heat exchanger with the hot concentrate coming from the concentrate collecting container.
The heat supply for the evaporation of the mixture of carrier gas and vapor into the wet mixture of carrier gas and vapor takes place through two evaporators/condensation heat exchangers by means of the compressed and cleaned mixture of carrier gas and dry vapor flowing from the concentrate separator unit that is able to condense at least partially in this evaporator/condensation heat exchanger through heat emission.
By means of such a method and device to carry out the method it is possible to reduce the overall energy expenditure considerably, since nearly all the hot currents are used to heat colder currents. Thanks to the two-step preheating of the waste liquid before it is conveyed to the admixing device, it is furthermore possible to adjust the temperature of the waste liquid exactly so that the dispersion of the waste liquid in the carrier gas is promoted by nearly spontaneous evaporation following the admixing of carrier gas.
In addition, the losses in carrier gas can be minimized considerably by the closed carrier gas circuit between the condensate separator unit and the carrier gas admixing device.
In spite of these advantages, still only certain liquid impurities can be separated. Again, in case of treatment fluids containing a plurality of liquid impurities having different boiling temperatures as well as a relatively large amount of gaseous impurities, the danger exists that a considerable portion of the liquid and/or gaseous impurities cannot be removed by this method so that they continue to contaminate the base liquid, generally water, even after the treatment. Due to the closed carrier gas circuit, the gaseous impurities furthermore increase here in an undesirable manner in the carrier gas circuit, especially when sea or brine water is to be treated in order to obtain drinking and/or service water, as a large quantity of CO2 are produced among other impurities, with the thermal decomposition of HCO3. In such a case, the installation must be stopped at regular intervals and the carrier gas must be freed of the gaseous impurities accumulated in the gas circuit because of the closed carrier gas circuit. This is not economical and reduces the effectiveness of the installation. Furthermore, such an upgrading for the sake of a longer running time of the installation requires a larger layout and dimensioning of the pipe conduits and devices, substantially increasing costs. Therefore this treatment method is also only suitable for a certain, relatively narrow spectrum of treatment fluids.
In addition, known distillation methods without the utilization of carrier gas as conveying gas are known from WO 87/07847 and WO 98/31445 and relate to a fundamentally different type of method whereby a water cleaning and water desalinization by means of vacuum distillation is carried out according to WO 87/07847, and fouling of the installation itself is to be avoided according to WO 98/31445.
Accordingly, it is therefore the object of the present invention to further develop a method and device for the treatment of liquids, by means of which an effective and economical treatment of treatment fluids containing a plurality of liquid impurities having different boiling temperatures and/or a large quantity of gaseous impurities, in particular the treatment of sea and/or brackish water of a waste liquid and/or waste water can be carried out.
This and other objectives and advantages of the present invention will become apparent from the following more detailed descriptions.